1. Field of the Invention
Embodiments of the invention relate to a device and a method for working in the presence of electromagnetic fields, in particular fields occurring in magnetic resonance tomography imaging devices. (“MRT” or “MRI” stand for magnetic resonance tomography and magnetic resonance imaging respectively, wherein these two acronyms are used interchangeably herein).
2. Description of the Related Art
Although MRI testing is becoming increasingly important in diagnostic medicine, it is contraindicated for some patients. Such contraindication may result from an active implanted medical device (also referred to below as “implant” or “IMD”). Besides MRI testing, however, other technical applications pose a risk to the user of medical devices or implantable medical devices, particularly when such applications generate strong electromagnetic interference fields (electromagnetic interference (EMI)) in their surroundings.
In order to still allow MRI testing or working in the surroundings of electromagnetic interference fields, various approaches are known which relate either to performing the MRI testing or to the implantable medical device.
Among others, technologies based on conventional processes for identifying magnetic fields are known for detecting magnetic fields. US 2008/0154342 describes a method which uses a giant magnetoresistance (GMR) sensor to detect problematic magnetic fields from MRT devices. However, these technological approaches are not very specific, and create increased energy requirements which result in a shorter operating period for equivalent energy reserves.
A further technological approach is the use of optical signal transmission instead of typical electrode lines based on electrical signal transmission. Use of these optical lines prevents the injection of electromagnetic interference fields from an MRI device into the electrode lines, but the overall system is more complex since on the one hand the electrical signals must first be converted to optical signals, and on the basis of the signals the stimulation pulses must be generated from the optical signals at the stimulation site, and on the other hand signals that are measured at the stimulation site must likewise be converted. As a rule, such higher-complexity systems also increase the energy requirements for an implant. Such a system based on optical signal transmission is described in US 2005/0090886 and U.S. Pat. No. 7,450,996.
In addition, a system is known from US 2002/0133204 and U.S. Pat. No. 6,901,292 which by selection of certain protective devices provides various modes for operating an electrical implant. A disadvantage of this system is that for high RF fields it also allows heating of the electrodes, since the focus of the cited documents is on electromagnetic compatibility with metal detectors and electronic security units.